There is a worldwide emphasis on expanding clean renewable energy sources. Solar energy is very abundant and harvesting that energy has been made more plausible by the continued development and improvement of photovoltaic cells and collectors in recent years. The cost of photovoltaic technology has declined significantly within the past decade, making it more affordable as an investment for the average homeowner. The electrical energy generated by these systems can either be used to supply local loads and/or integrated with a public utility grid, which may pay for the energy. In either case, a homeowner can realize a significant savings on electrical energy use. With the cost of photovoltaic systems continually falling, the payback period on an investment in a photovoltaic system is becoming shorter and shorter. To maximize the return on investment, a homeowner may increase the total power capacity by efficiently tiling a roof with as many photovoltaic collectors as possible.
Several types of photovoltaic collectors exist including solar cells, solar cell arrays, thin film photovoltaic, and others. Since all of these type collect energy from sunlight, such collectors will be referred to generally in this disclosure as “solar collectors.”
An assembly of solar collectors on a roof often is traditionally called an array. The collectors within the array are designed to capture electromagnetic energy from the sun and convert this energy into direct current (DC) electrical energy. One standard wiring technique sometimes used within such an array is a combination of series and parallel connections to produce a desired DC voltage or “electrical energy” from the array. The DC electrical energy may be coupled to a remotely located main inverter that converts the DC electrical energy into the alternating current (AC) electrical energy required to integrate with a public utility grid or power home appliances. This traditional method of installation requires significant planning to insure that the voltage generated and current rating of the array are compatible with the inverter's operating specifications. This, in turn, requires knowledge of series and parallel electrical connections, and how to combine them within the photovoltaic array to produce a specific desired electrical output. This method also can pose a significant safety hazard since the DC outputs of the solar collectors are live during installation and can increase as additional collectors are added to the array to produce the final voltage and current capacity (i.e. the power rating) of the array. Another issue with DC arrays feeding a central inverter is that if one collector within a series or string of collectors is defective or becomes shaded, the DC voltage generated by the string of collectors is reduced or otherwise affected, which can cause problems at the central inverter.
Micro-inverters have been developed in recent years to address the safety issues, system design confusion, and performance issues related to DC solar collector arrays. Micro-inverters convert DC electrical energy from individual collectors or groups of collectors to AC electrical energy. DC-to-AC conversion thus occurs at the collector level rather than at the array level. The power matching between a collector and a micro-inverter is defined when selecting and purchasing collectors and inverters, and an installer need not be concerned with such matching issues. Once a collector's DC output is converted to AC, the connection between collectors within an array are simple parallel connections, making the array much easier to install. Moreover, once coupled to a solar collector, a micro-inverter will not produce electrical energy until directed to do so by a command code. This reduces the risk of electrical shock to installers, improving further the safety of installation. Furthermore, since the inversion is carried out at the collector level, if a solar collector or a nano-inverter fails, is defective, or shaded, the AC voltage produced by the array remains unchanged, albeit with perhaps slightly reduced current capacity.
A recent trend in the roof mounted photovoltaic industry is to offer a micro-inverter already mounted and wired to a photovoltaic collector to produce an “AC collector.” Such AC collectors eliminate the need for mounting or connecting the inverters to the DC outputs of their collectors in the field. This can improve installation time and can add an even greater level of safety since an installer is not exposed to any live electrical energy during installation. Micro-inverters available for use in such typical large AC collectors, however, are typically optimized to operate at a collector's standard maximum power rating, which usually is between 190 Watts and 280 Watts. Since these micro-inverters operate at such high power, they tend to generate significant heat due to electrical resistance during operation, and therefore require sufficient air space and ventilation to dissipate the heat. This often requires the typical AC collector array to be raised above a roof deck by two to four inches, which some consider aesthetically unpleasing on a residential home. In addition, the standard AC collectors are generally large in size (3′×5′) and this can pose aesthetic as well as installation problems. For instance, the large size generally limits the number of collectors that can fit on a given roof and can make handling and installation difficult on steep sloped roofs, especially in windy conditions.
There is a need for a much smaller AC solar roof shingle that resembles traditional roof shingles in size and shape and that can be installed directly on a roof deck and integrated into a field of standard shingles with aesthetically pleasing results. Such a roof shingle should operate efficiently with minimum required ventilation around the inverters of the collectors. It is to the provision of such a solar roof shingle and a solar roof system incorporating same that the present invention is primarily directed.